Folded sigma-shaped dipole antenna



Aug. 4, 1964 v. T. NORWOOD 3,143,737 FOLDED S-SHAPED DIPOLE ANTENNAFiled Aug. 3, 1962 FIG.2.

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SOURCE INVENTOR VIRGINIA r. uoawooo g BY SOURCE ATTORNEY United StatesPatent Office 3,143,737 i 'atented Aug. 4, 1964 3,143,737 FOLDEDS-SHAPED DIPOLE ANTENNA Virginia T. Norwood, Los Angelles, Calif.,assignor, by mesne assignments, to the United States of America asrepresented by the Secretary of the Navy Filed Aug. 3, 1962, Ser. No.214,777 7 Qlairns. (431. 343797) This invention relates to a radiofrequency antenna, and more particularly to a radiating antenna of thefolded dipole type of an S-construction which is capable of being fed bya balanced open-wire line lying in the plane of polarization of theradiated power.

One of the most common and simple methods of feeding a multiple array ofantennas is the use of a balanced open-wire line to carry the radiofrequency energy from the source to each of the spaced antennas. Thebalanced open-wire line consists of a pair of straight conductorsforming a transmission line. These conductors would lie in a horizontalline below the antennas. Vertical conductors from each of thesehorizontal conductors then carry the energy from the transmission lineto the appropriate feed points on each of the radiating antennastructures, which are so spaced and oriented with respect to one anotheras to give the desired radiation pattern.

If each of the radiating antennas of an array is of the dipole or foldeddipole configuration, the arms thereof extend horizontally, but in ahorizontal direction perpendicular to the direction of the balancedopen-wire line. In such an array, the balanced open-wire line will alsobe perpendicular to the polarization of the energy radiated from each ofthe antenna elements.

In some situations it becomes desirable to employ a pair of suchmultiple antenna arrays with one array having a polarizationperpendicular to that of the other array; this is known as crosspolarization. Thus the energy from one array will be radiated in adirection perpendicular to the direction of radiation from that of theother array. The signals from one array will not be received by theantennas of the other array since the arms do not lie in the directionof polarization of those signals. However, the open-wire line feedingeach array will be extended in the direction of polarization of theother array of antennas and can be expected, unless shielded, to receivesubstantial quantities of the radiation transmitted from that otherarray resulting in interference between the two with the signal to betransmitted therefrom. Should a circumstance occur in which this mutualinterference were undesirable or intolerable, it would be necessary toprovide shielding of each of the open-wire lines from the radiatedenergy of the opposite array.

It is an object of the present invention to provide an antennaconfiguration having essential characteristics of a folded dipoleantenna which may be fed from an openwire line which lies in the planeof polarization of the radiated energy.

Another object of this invention is to provide a new and improvedantenna for radiating radio frequency energy in the manner of a foldeddipole.

A further object of this invention is to provide a novel antenna array,which may be constructed from a plurality of antennas having a novelconfiguration.

Various other objects and advantages will appear from the followingdescription of the several embodiments of the invention, and the mostnovel features will be particularly pointed out hereinafter inconnection with the appended claims.

In the drawing:

FIG. 1 is a pictorial representation of the basic antenna configurationaccording to the invention;

FIG. 2 a pictorial representation of a modification of the basicconfiguration of the antenna of the present invention;

FIG. 3 is a representation of a multiple antenna array employing thebasic antenna configuration with a balanced open-wire feed line; and

FIG. 4 is an illustration of the top view of a composite antenna arraycomposed of a pair of arrays of the type shown in FIG. 3, which areorthogonally arranged and polarized with respect to one another.

In FIG. 1, is shown the basic antenna structure 10 in which a conductivemetallic strip 11 is bent in the manner of a flattened S to form theradiating element of the antenna. The flat S-shape has an elongatedcenter portion, which is approximately one wavelength long for mostefficient operation; this center portion may vary, however, as inconstruction of the normal folded dipole antenna, from aboutthree-quarters to one and a quarter wavelengths to give efiicientoperation in radiating the radio frequency energy of a particularfrequency. The end portions of the radiating strip 11 are bent back uponthe center portions on opposite sides thereof to form the fiat S-shape.These end portions extend to approximately the mid point of theelongated center strip where they are attached dividually to a pair ofperpendicular coupling strips 12 and 13 to form the feed points of theantenna. The coupling strips 12 and 13 feed the radio frequency energyto the radiating strip 11 from which it is radiated into the surroundingspace. It is to be noted that the mode of operation of the presentantenna in many ways parallels that of the simple folded dipole. Theenergy fed to each of the folded end portions excites the center portionto produce fields thereon in exactly the same manner that the shortportions of the folded dipole connected to the feed points induce acurrent in the continuous element connected thereto. However, it is tobe noted that the feed points on the instant S-shaped antenna arelocated on a line perpendicular to the elongated direction of theantenna whereas in the folded dipole the two feed points lie oppositeone another in a line parallel to the elongation of the antenna element.Since the direction of polarization of the radiated energy is in thedirection of elon ation, the feed points in the instant antenna lieathwart the direction of polarization Whereas in the normal foldeddipole they lie in the same direction as polarization.

It should also be noted that the configuration allows the polarizationof the radiated energy to be rotated degrees without changing the feedpoints by simply using a radiating element in which the conductiveradiating strip 11 is bent in backward fashion. The advantage of thisfeature will be later explained in more detail.

The antenna It may be constructed with a dielectric material 14 to fillin the spaces between the center conductor elements and the two outsideportions of the elements in order to form a more rugged antennastructure, as commonly known in the art. The reactance of the instantradiating elements may be controlled by varying one or more of severalparameters, such as the length of the radiating elements along thedirection of the elongation, the width of the conductive strip, and byusing materials for the dielectric filling 14 having differentdielectric constants, all of which are well known in the art. Alsovariations in the resistance of the antenna can be accomplished bychanging the spacing between the inner conductor and the two outerportions of the conductor in accordance with known principles applicableto folded dipole antennas, or by metallic loading at the feed points.

In addition to the well known methods of changing the impedance ofantennas of the folded dipole varieties, this antenna configurationprovides an additional method which may be employed. This additionalmethod, as

illustrated in FIG. 2, consists of removing some or all of the innerconductor in the region between the feed points of the antenna. This maybe done by cutting a notch 15 in the normally uniform antenna strip, asillustrated, or even by completely removing that portion of the strip.By thus varying the width of the metallic strip in this region, theshielding between the terminals is lessened and the impedance of theantenna is greatly increased. Obviously the impedance may also bedecreased by increasing the width of the strip between the feed points.In each case an appropriate line length correction or an addition ofmetal blocks at the terminal points should be inade to maintain theresonance of the antenna input. In this manner the impedance of theantenna can be made to range from high levels of 400 ohms to low levelsof 75 ohms by simply changing the width of the strip in the region ofthe feed terminals. Similar changes may also be made by varying thethickness instead of the width of the conductive strip between the twofeed terminals.

In FIG. 3, three S-shaped antennas 16, 17 and 18 are fed by an open wireline 19, which extends from a source of radio frequency energy 21. Theantennas are spaced along the open-wire line 19 in such a manner as togive a desired radiation pattern for the radio frequency energy. In eachcase the antennas 16, 17 and 18 are fed from the open-wire line and arepolarized in the direction of the open-wire line 19. This is donewithout the necessity of bending or twisting the vertical feed elementextending from the open wire line 19 to each of the antenna feed points.In the illustration of FIG. 3, the center antenna element is mounted ina mirror image or backward 8 fashion as compared with each of the endantenna elements 16 and 13. As aforementioned, this provides a 180degree phase shift in the radiated signal from this antenna 17 asdistinguished from that which would ordinarily be produced by thespacing of the antennas along the open wire feed line 19. Thisaccomplishes a result which could be obtained with the normal foldeddipole only by feed line cross over or by a phase adjustment along thefeed line.

In FIG. 4, a pair of multiple antenna arrays 22 and 23 are showndisposed in orthogonal relation to one another. The energy radiated bythe antenna elements of the array 22 will have a polarization which isperpendicular to that of the polarization of the multiple array 23.Thus, due to the orthogonal polarization, the energy radiation from onearray does not interfere with that from the other array nor do theantenna elements receive any substantial portion of the energy radiatedfrom the other array. In addition, the S-shaped antennas permit theopen-wire lines feeding each of the arrays to be in orthogonal relationto the radiated energy from the opposite array. Therefore, one array maybe operated in time coincidence with the other without either arrayreceiving or interfering with the radiation of the opposite array eitherin the antenna elements or the openwire line feeding these elements. Nosubstantial portion of either array or its feed lines will be in thedirection of polarization of the other.

Thus, it may be seen that the normal configuration of the S-shapedantenna of the present invention provides a radiating antenna elementhaving radiation characteristics similar to the normal folded dipole buthaving certain novel advantages thereover.

It will be understood that various changes in the details, materials,and arrangements of parts, which have been herein described andillustrated in order to explain the nature of the invention, may be madeby those skilled in the art, within the principle and scope of theinvention as claimed in the appended claims.

What is claimed is:

l. A radio frequency radiating antenna comprising a conductive elementhaving a straight central portion, a pair of elongated straight portionsparallel to said central portion and on opposite sides thereof, one endof each of said pair being conductively joined to an opposite end ofsaid central portion and the other end of said pair being adapted to beconnected to the terminals of a source of radio frequency energy, saidother ends being adjacent one another on opposite sides of said centralportion.

2. The antenna of claim 1 further comprising a solid dielectric materialfilling the area between each of said pair and said central portions.

3. A radio frequency radiating antenna comprising a radiating portioncomposed of a conductive strip, a pair of terminals at each end of saidstrip adapted to receive radio frequency energy to be radiated, saidstrip being bent upon itself in a single plane to form an S-shape havingan elongated central portion and a pair of elongated end portionsparallel to said central portion and on opposite sides thereof, saidcentral portion being approximately three-quarters to one and a quartertimes the wavelength of the radio frequency energy to be radiated, saidpair of terminals being adjacent the same point on said central portionon opposite sides thereof, whereby radio frequency energy received atsaid terminals is radiated with a polarization parallel to saidelongation in folded dipole fashion.

4. An antenna array comprising a plurality of antennas, each of saidantennas comprising a conductive element having a straight centralportion, a pair of elongated straight portions parallel to said centralportion and on opposite sides thereof, one end of each of said pairbeing conductively joined to an opposite end of said central portion andthe other ends of said pair being adapted to be connected to theterminals of a source of radio frequency energy, said other ends beingadjacent One another on opposite sides of said central portion, abalanced open-Wire feed line disposed parallel to said elongatedstraight portions of said antennas, and a plurality or pairs of couplingconductors disposed at right angles to said open-wire feed lineconnecting one of said terminals of each of said antennas to arespective one of said openwire feed lines.

5. An orthogonal radio frequency radiating arrangement comprising a pairof antenna arrays comprising a plurality of antennas, each of saidantennas comprising a conductive element having a straight centralportion, :a pair of elongated straight, portions parallel to saidcentral portion and on opposite sides thereof, one end of each of saidpair being conductively joined to an opposite end of said centralportion and the other ends of said pair being adapted to be connected tothe terminals of a source of radio frequency energy, said other endsbeing adjacent one another on opposite sides of said central portion, abalanced open-wire feed line disposed parallel to said elongatedstraight portions of said antennas, and a plurality of pairs of couplingconductors disposed at right angles to said open-wire feed lineconnecting one of said terminals of each of said antennas to arespective one of said open Wire feed lines,.said elongated portions ofthe antennas and the open wire transmission lines of each of said arraysbeing perpendicular the elongated portion the antennas and the open-wiretransmission line of the other array, whereby the antennas and feedlines of each array are orthogonally polarized to that of the otherarray.

6. A radio frequency radiating antenna comprising a radiating portioncomposed of a conductive strip, a pair of terminals at each end of saidstrip adapted to receive radio frequency energy to be radiated, saidstrip being bent upon itselfin a single plane to form an S-shape havingan elongated central portion and a pair of elongated end portionsparallel to said central portion and on opposite sides thereof, saidcentral portion being approximately to 1% times the wave length of theradio frequency energy to be radiated, said pair of terminals beingadjacent the same point on said central portion on opposite sidesthereof, the portion of said conductive strip in the vicinity of saidsame point having difierent crosssectional area from the remainder ofthe conductive strip, whereby radio frequency energy received at saidterminals is radiated with the polarization parallel to said elongationand folded dipole fashion.

7. A radio frequency radiating antenna comprising a radiating portioncomposed of a conductive strip, a pair of terminals at each end of saidstrip adapted to receive radio frequency energy to be radiated, saidstrip being 10 bent upon itself in a single plane to form an S-shapehaving an elongated central portion and a pair of elongated end portionsparallel to said central portion and on opposite sides thereof, saidcentral portion being approximately to 1% times the Wave length of theradio frequency energy to be radiated, said pair of terminals beingadjacent the same point on said central portion on opposite sidesthereof, a portion of said conductive strip in the vicinity of said samepoint being removed, whereby radio frequency energy received at saidterminals is radiated with the polarization parallel to said elongationand folded dipole fashion.

References Cited in the file of this patent UNITED STATES PATENTS2,505,098 Cornelius Apr. 25, 1950 3,025,524 Thies Mar. 13, 1962 FOREIGNPATENTS 289,640 Italy Oct. 22, 1931 560,461 Canada July 15, 1958

1. A RADIO FREQUENCY RADIATING ANTENNA COMPRISING A CONDUCTIVE ELEMENTHAVING A STRAIGHT CENTRAL PORTION, A PAIR OF ELONGATED STRAIGHT PORTIONSPARALLEL TO SAID CENTRAL PORTION AND ON OPPOSITE SIDES THEREOF, ONE ENDOF EACH OF SAID PAIR BEING CONDUCTIVELY JOINED TO AN OPPOSITE END OFSAID CENTRAL PORTION AND THE OTHER END OF SAID PAIR BEING ADAPTED TO BECONNECTED TO THE TERMINALS OF A SOURCE OF RADIO FREQUENCY ENERGY, SAIDOTHER ENDS BEING ADJACENT ONE ANOTHER ON OPPOSITE SIDES OF SAID CENTRALPORTION.